Question

Which of the following are not correct?
A) The basic unit of time is second.
B) Every object moves with a constant speed.
C) Distance between two cities is measured in kilometers.
D) The time period of a given pendulum is not constant.
E) Speed of the train is expressed in m/h.

Answer 1

The above options shows different formula and scenarios where specific units and quantities are used and now to find the correct unit and quantity we need to check every option one by one, you can use real world knowledge as well to determine the correctness of the statements given above.

Complete solution:
Let us check the first option, the first option states that second is the basic unit of time, there is a difference between smallest and basic. Basic means the lowest unit that is used in the real world scenarios and can be easy to use by the general public as second is the most basic time period used whether to calculate time or any other time related calculation; we can say that second is basic unit of time.
Second option, every object moves with a constant speed is false as imagine driving a car at a constant speed in the real world is impossible as one needs to apply brake or change speed when passing or changing lanes hence, the statement is false.
Third option, distance between two cities is measured in kilometers is true as the eastern part of the world where the highest distance in road or air is measured in kilometer even if the distance is less than one kilometer, it is still mentioned in kilometer hence, the statement is true.
Fourth option, the time period of a pendulum can’t be constant as the time period of the pendulum depends upon mass, gravity and even temperature which changes time to time hence, the statement is false.
Fifth option, the speed of any moving object is described by measuring distance upon time and when the distance is in kilometers we use time as hour or $h$ and when in meter than seconds.

Therefore, the correct options are A and C.

Note: Option B and D might be true if the conditions were ideal and not real as for distance measurement between cities in western world except Europe is calculated in miles. And to convert the speed from \km/h\ to \m/s\ or vice versa we multiply it by $\dfrac{5}{18}$ and $\dfrac{18}{5}$ respectively.